In typical vacuum toilet assemblies, such as are used in boats and recreational vehicles, as shown by U.S. Pat. No. 5,621,924, and co-pending applications Ser. Nos. 08/551,029 filed Oct. 31, 1995 and 08/839,267 filed Apr. 17, 1997 (the disclosures of which are hereby incorporated by reference herein), the pump for creating the vacuum reservoir in an air tight tank (either a simple vacuum tank, or a combined vacuum and sewage holding tank) must be able to pump sewage waste (liquid with a large amount of solids) in addition to pumping air to create the vacuum. That means that the pump must be of fairly high quality, and typically includes a significant number of metal interior components in order to be effective. However in vacuum toilet systems associated with vehicles, such as boats and recreational vehicles, it is desirable to reduce the weight of the vacuum toilet assembly, and it is of course also desirable to make it less expensive.
According to the present invention a vacuum toilet assembly is provided, and particularly a reciprocating diaphragm air pump associated with the vacuum toilet assembly, which contains substantially all plastic or rubber internal components so that it is relatively light in weight, and relatively inexpensive. The air pump according to the invention is used solely to withdraw air from the vacuum holding tank, and is particularly desirable for use with a combined vacuum and sewage holding tank. While the pump can pass water in emergency situations without damage, it is designed specifically for use with air alone, and therefore can have a lighter construction.
The ability of the pump of the invention to pull vacuum and pump water makes it unique among commercial pumps. In practice water pumps are poor vacuum pumps and vacuum pumps are poor water pumps. The pump of the invention, however, because of its unique design (including reinforced die-cut flat elastomeric material disk valve elements, all non-metallic interior cavity, and particular stroke with optimized stroke versus performance characteristics) is an excellent vacuum pump yet unlike other good vacuum pumps will not seize if it encounters an incompressible fluid like water. The pump cavity has good vacuum efficiency yet will not be overstressed if it is necessary to pump water.
According to one aspect of the present invention a vacuum toilet assembly is provided. The assembly comprises: A vacuum toilet. A vacuum tank operatively connected to the vacuum toilet so as to provide a source of vacuum to remove waste from the toilet when the toilet is flushed. An air pump connected to the vacuum tank for removing air from the vacuum tank to create a partial vacuum therein, the air pump having an inlet conduit connected to an upper portion of the tank, and an outlet. And, a sound muffler and an odor filter operatively connected to the air pump outlet, or a sound reducing check valve.
The sound muffler and odor filter may comprise a combined muffler and filter, such as a conduit suction having activated charcoal therein. For example the muffler may keep sound emissions below 65 decibels. The muffler preferably is, for example, a 0.625 inch outside diameter tube about six inches long and filled with activated charcoal, which captures odor. The combined muffler/filter can be placed anywhere in the discharge line (e.g. hose, conduit, or the actual outlet itself) of the air pump outlet. Alternatively a rat-tail check valve is used which allows air to exit the pump, but none to enter, yet also serves as a noise suppressor. Even if foreign material fouls the main valves the check valve will prevent vacuum loss.
The vacuum tank preferably is a combined vacuum and holding tank, such as shown in pending applications Ser. Nos. 08/551,029 filed Oct. 31, 1995 and 08/839,267 filed Apr. 17, 1997 (atty. dkt. 19-125). All of the internal pump components are preferably plastic or rubber, with the exception of perhaps a fastener and diaphragm backup plate, and the pump can be mounted anywhere desirable. Using plastic for the internal pump components not only prevents rust, but reduces the weight of the pump. The pump may be mounted directly on the vacuum/holding tank, as by using a stainless steel bracket. While the pump is designed to pump only air it can pass water without damage, and operates very effectively in the humid conditions to which it is subjected.
The air pump preferably comprises a powered reciprocating diaphragm pump, having a reciprocating diaphragm. The diaphragm pump may also comprise a housing having first and second oppositely directed disk valves therein, having a first disk valve element and a second disk valve element. The diaphragm pump housing may comprise a central housing portion having the inlet and outlet therein, with a first dividing wall substantially parallel to the direction of movement of air between the inlet and the outlet. A second dividing wall may prevent direct flow of air between the inlet and the outlet. Typically the first dividing wall will be generally horizontal and the second dividing wall will be generally vertical in the standard mounting of the pump. The first dividing wall has a plurality of first perforations associated with the first disk valve element and a plurality of second perforations associated with a second disk valve element, the disk valve elements cooperating with concave perforated portions of the first dividing wall. The first dividing wall also preferably has a sealing surface engaging the reciprocating diaphragm, the sealing surface having a plurality of sealing rings thereon. The disk valve elements may be connected to the first dividing wall by canoe clips in oppositely directed blind bores formed in the first dividing wall.
Typically the reciprocating diaphragm has a total stroke length of about 0.3-0.33 inches [0.75-0.85 cm], e.g. with a 0.156 inch [0.4 cm] half-stroke or 0.312 inch [0.8 cm] full stroke, to create a vacuum and expel removed air. The pump is capable of achieving about 10 inches [25.5 cm] mercury of vacuum in an empty 9.5 gallon vacuum tank in roughly one minute, yet can pump at least about five liters of water per minute if necessary (e.g. about 7-8 l./min.). Where a combined vacuum/holding tank is provided, of course as the tank fills with sewage liquid, the amount of time for creating the necessary vacuum for it to act as a vacuum reservoir is significantly reduced.
Any suitable motor and mechanical connection may be provided for effecting reciprocation of the diaphragm. For example a direct drive 12 volt D.C. motor, typically operating at a speed of about 2100-2600 rpm, preferably about 2300 rpm (a speed giving adequate performance and relatively low sound emission, i.e. having an optimized noise versus performance ratio), may be used as the power source for powering reciprocation of the diaphragm. The diaphragm is typically of any suitable flexible material such as natural or synthetic rubber (e.g. nitrile rubber), or various plastics (such as a copolymer of polypropylene and polyethylene), and may have top and bottom stainless steel backing plates. The diaphragm and plates may be connected to a connecting rod at one end thereof, the other end of the rod having a pressed in ball bearing. Pressed into the inner race of the ball bearing may be an eccentric which creates the 0.156 inch half stroke. However any other suitable conventional mechanism may be provided for effecting the reciprocation of the diaphragm.
The central housing portion preferably has a tapered volume defined between the diaphragm and the first dividing wall. The volume has an area adjacent the first dividing wall of about 83-93% (e.g. about 88%) of the area adjacent the diaphragm when it is in a central position intermediate the end of its stroke. This increases pump efficiency, and combined with the preferred stroke length and motor rpm set forth above, provides an optimized noise/efficiency ratio.
According to another aspect of the present invention a reciprocating diaphragm air pump per se is provided. The air pump comprises the following components: A central housing portion having the inlet and outlet therein, a first dividing wall substantially parallel to the direction of movement of air directly between the inlet and outlet and having first and second opposite surfaces each having a concave portion, and a second dividing wall preventing direct flow of air between the inlet and the outlet. A first elastomeric disk valve element engaging the concave portion of the first surface, and a second elastomeric disk valve element engaging the concave portion of the second surface. The first dividing wall having a plurality of first perforations extending between the first and second surfaces and associated with the first disk valve element, and a plurality of second perforations extending between the first and second surfaces and associated with the second disk valve element. And, a powered reciprocating diaphragm movable in a direction generally perpendicular to said first and second surfaces to cause air flow through the first perforations when the diaphragm moves away from the first and second surfaces, and to cause air flow through the second perforations when the diaphragm moves toward the first and second surfaces.
The details of the reciprocating diaphragm pump are as described above with respect to the vacuum toilet assembly.
According to a still further embodiment of the present invention, a reciprocating diaphragm air pump per se is provided comprising the following components: A central housing portion having the inlet and outlet therein. First and second oppositely directed check valve elements associated with the housing portion. A powered reciprocating diaphragm movable in a first direction to cause air flow through the first check valve but not the second check valve, and in a second direction, opposite to the first direction, to cause air flow through the second check valve but not the first check valve. Wherein the air pump is capable of achieving about ten inches [25.5 cm] Hg of vacuum in an empty 9.5 gallon [38 liter] vacuum tank in roughly one minute, and it can pump more than a liter (actually more than 5 liters) of water per minute, if necessary. And, wherein the reciprocating diaphragm has a total stroke length of about 0.3-0.33 inches.
The first and second check valves are preferably oppositely directed elastomeric disk valve elements, cooperating with perforated concave surfaces. Except for drive components, substantially all of the pump components are plastic or rubber. The rest of the details of the pump may be as described above.
It is the primary object of the present invention to provide an advantageous vacuum toilet assembly, and a reciprocating diaphragm air pump for use therein. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.